Invisible invisible information detecting apparatus and method

Abstract: An object of the present invention is to provide an invisible information recorded medium having an identification mark. In order to achieve the object, an invisible information recorded medium is provided having an identification mark recorded thereon, the identification mark being composed of a region having a high reflectance and a region having a low reflectance as compared with the reflectance of the medium in the same near infrared ray region.

Description: The present invention relates to an apparatus and method for detecting copy-prohibited documents having thereon an invisible identification mark. Hitherto, the trend of improving the performance of copying machines arises a risk of forgery of bills, securities and notes and the like. Therefore, there arises a necessity of judging whether or not forgery of the bill or the like has been performed. Further, the forgery of the bills must be previously detected and prevented. In order to prevent the forgery, there have suggested a marking method using a ultraviolet ray exciting fluorescent pigment, a method using a diffraction phenomenon such as hologram, a method of applying a magnetic substance to be detected by a magnetic head, a method using color change occurring due to photochromism and a method of discriminating a specific image, such as a bill, by image recognition. With the improvement in the performance of the copying machine and so forth, copying of various information items can easily be performed. On the other hand, privacy guarding and trade secret confidence have been considered important, causing a problem to arise in that copying can easily be performed. Hitherto, the foregoing copying has been prevented by bonding a special film to the document or the like to cause the copied image to be deteriorated or to cause the forgery to be informed. Forgery copying has been prevented by a method comprising the step of bonding a special film to the document or the like to deteriorate the quality of the copied image or a method of clearing the forgery copying. However, the method using the ultraviolet rays exciting fluorescent pigment encounters a problem in that a countermeasure can be taken because the fluorescent pigment can easily be detected by an ultraviolet irradiation means, such as a black lamp. Further, the necessity of using a ultraviolet ray source in the apparatus makes the optical system to be complicated. The method using the diffraction phenomenon, such as hologram, encounters a problem in that the formation of the mark on the bill or the like raises the cost. The method of applying the magnetic substance arises a necessity of bringing the bill or the like into contact with the magnetic head in a hermetical manner, causing a problem to arise in that the structure to be complicated. The method using photochromism suffers from instability of the photochromism compound. The method based on the image recognition requires a large quantity of data to recognize all bills and securities and so forth, causing a heavy load to be burden by the apparatus and the cost to be enlarged. Another method using near infrared fluorescent has been disclosed to overcome the foregoing problems, so that a long life light emitting diode is enabled to be used, and therefore an influence of contamination can be prevented satisfactorily. If the near infrared ray absorbing film or the like is used between the detecting apparatus and the original document, there arises a problem in that the detection cannot easily be performed. The necessity of individually using a light emitting diode and a photodiode sensitive to long wavelength causes the structure of the apparatus to be complicated. However, each of the foregoing conventional methods has been structured to correspond to analog copying machines. Therefore, it has been difficult to prevent the forgery copying and reading in a copying machine or a printer comprising a reading unit using a CCD or the like. Therefore, it is preferable that the detection apparatus identifies that the recorded medium is the copy and read inhibited medium to stop the operation. Each of the foregoing identifying marks has a problem. However, each of the foregoing conventional methods has been structured to correspond to analog copying machines. Therefore, it is unsatisfactory to realize secret confidence with a copying machine or a printer comprising a reading unit using a CCD or the like. The fact that the easy recognition arises a problem in that an effective secret confidence method has not been realized against reproduction writing and photography. JP-A-608880 discloses a system to prevent copying of documents by treating the sheets of the confidential documents the copying of which is undesirable, with an IR absorber or a metal in advance, and detecting change of a transmitted amount of IR rays. WO-A-92/04192 discloses a method for providing intelligible markings that are virtually invisible to the unaided eye on the surface of an article, comprising applying onto the surface, by a jet printing process, a marking medium comprising a compatible liquid or viscous substance containing an organic laser dye that is poorly absorptive of radiation in the visible range of about 400 to 700 nanometres, is highly absorptive of radiation in the near infrared range of at least about 750 nanometres in wavelength (typically about 750 to 900 nanometres), and fluoresces in response to radiation excitation in the said near infrared range to produce fluorescent radiation of wavelengths longer than the wavelength of the excitation (typically in the range of about 800 to 1100 nanometres). The present invention is directed to the foregoing problems. According to the present invention, there is provided an apparatus for detecting copy-prohibited documents as set out in claim 1. The present invention also provides a method of detecting copy-prohibited documents as set out in claim 5. Optional features are set out in claims 2 to 4 and 6. BRIEF DESCRIPTION OF THE DRAWINGS Fig 1 illustrates reflection spectrum of a medium having an identification pattern recorded thereon; Fig 2 is a structural view which illustrates a color copying apparatus in an embodiment; Fig. 3 illustrates a spectrum reflectance of a standard white plate; Figs 4A and 4B are structural views which illustrate a CCD according to the first embodiment of the present invention; Fig. 5 illustrates characteristics of a dichroic filter for cutting infrared rays; Fig. 6 is a view which illustrates a state where an infrared ray cutting glass is fastened to a CCD sensor; Fig. 7 is a view which illustrates a fastened cover glass in a case where the glass for cutting infrared rays is disposed on the cover glass of the CCD; Fig. 8 are graphs which illustrate spectral sensitivity characteristics of a visible line sensor and characteristics of a filter for an infrared ray reading sensor; Fig. 9 illustrates a spectrum transmission ratio of a specific pattern; Fig. 10 illustrates characteristics of a filter for cutting far infrared rays; Fig. 11 is comprised of Figs. 11A and 11B and illustrate an image signal control portion; Fig. 12 is a timing chart of an image control signal; Figs. 13A and 13B are structural views which illustrate a specific original document identification pattern for detection in an embodiment of the present invention; Figs. 14A and 14B illustrate absorption spectrum and fluorescent spectrum of an ink (fluorescent coloring material) for use in a high reflectance portion of the specific pattern; Fig. 15 is a 2D-area signal generating portion for use in detecting the specific pattern in the first embodiment of the present invention; Fig. 16 illustrates a reference pixel for use in detecting the specific pattern in the first embodiment of the present intention; Fig. 17 is a structural view which illustrates a specific pattern judgment portion in the first embodiment of the present invention; Fig. 18 is a flow chart for control performed by a CPU; Figs. 19A and 19B are structural views which illustrate an image reading apparatus according to a second embodiment of the present invention; and Figs. 20A and 20B are structural views which illustrate an image reading apparatus according to a third embodiment of the present invention. First Embodiment This embodiment is arranged in such a manner that a invisible information recorded medium having an identification mark, which is composed of a region having a relatively high reflectance as compared with the reflectance of a medium at the same near infrared wavelength and a region having a low reflectance, and an apparatus for detecting the medium are used to assuredly judge a specific original document with a low cost. Further, the specific original document can be judged while preventing an erroneous recognition in a case where a judgment prevention is performed while using an infrared ray absorption film or an infrared reflective film. The operation of recording the region will now be described which has a higher reflectance as compared with the reflectance of a medium and arranged to be used to record an identification mark having invisible information recorded for recognizing bills, securities and notes and the like (copy inhibited original documents which are subjects of the forgery inhibition) and inhibiting copying of them. Fluorescent coloring material or pigment is dissolved or dispersed in a binder so that a predetermined pattern is formed on the copy inhibition original document by printing or the like. The fluorescent coloring material or pigment may be a material having the fluorescent wavelength peak in a range of 700 nm or longer, preferably 750 nm or longer. Since the material having the fluorescent wavelength peak in a range of 700 nm or shorter can be visually detected, the secrecy cannot satisfactorily be maintained. If a material having the fluorescent wavelength peak in a range of 1100 nm or longer is used, sensitivity of a Si-type photo-detection device, such as a CCD, deteriorates. In this case, the identification mark cannot accurately be judged. It is further preferable to employ a fluorescent coloring material or pigment having the fluorescent wavelength peak in a range of 1000 nm or shorter. Since the near infrared fluorescent rays can be detected when they are separated from exciting rays, it is preferable that the two types of the rays have wavelengths which are considerably different from each other. Therefore, near infrared fluorescent coloring material or pigment and exciting rays are selected such that they are different from each other by 50 nm or more, preferably 100 nm or more. The exciting wavelength is selected depending upon the type of the light source and the spectral filter. The near infrared fluorescent coloring material may be a xanthene, oxazine, thiazine, polymethine or stryl compound. As an inorganic compound, a solid laser material of a type containing a rare earth element is used. More specifically, any one of the following near infrared fluorescent coloring material may be used. However, a material may be used regardless of the exemplified materials if it has fluorescent rays in the near infrared ray region and exhibits excellent fluorescent quantum yield, weather and light resistance. Compounds (1) to (61) The binder resin for use in the foregoing near infrared fluorescent coloring material or pigment may be a urea resin, melamine resin, alkyd resin, acryl resin, vinyl chloride resin, aromatic sulfonamide resin, or a benzoquanamine resin or their copolymer. By using a ultraviolet absorber or an anti-oxidant with the foregoing resin, the light resistance of the resin can be improved. The binder resin can be manufactured by a block resin crushing method, emulsification polymerizing method or a resin precipitation method or the like. (23) NdP 5 O 14 (24) LiNdP 4 O 12 (25) Na 5 Nd(WO 4 ) 4 (26) Al 3 Nd(BO 3 ) 4 (27) Cs 2 NaNdCl 6 (28) Li (Nd 0.9 Yb 0.1 ) P 4 O 12 (60) Nichia Chemical Industry NP-870 λ abs 250nm (61) LiAlO 2 : Fe 3+ λ abs 250nm The material of a type in which the near infrared fluorescent coloring material is dispersed or mixed in the binder may be used while being combined with a usual coloring material or pigment. It is preferable that the usual coloring material or pigment to be used while being combined do not absorb the exciting wavelength for the near infrared fluorescent coloring material. If the exciting wavelength for the near infrared fluorescent coloring material or pigment is not included in the visible ray region, covering with the usual coloring material or pigment or white pigment is able to improve the confidentiality of the copy prevention function. The region which has a lower reflectance as compared with the reflectance of the medium and arranged to be used to record an identification mark having invisible information recorded for recognizing bills, securities and notes and the like (copy inhibited original documents which are subjects of the forgery inhibition) and inhibiting copying of them is formed by dissolving or dispersing the color material or pigment which is absorbed in the infrared ray region and by printing a predetermined pattern in the copy-inhibited original document. The near infrared absorption coloring material or pigment can be a material having the absorption wavelength peak in a region of 700 nm or longer, preferably 750 nm or longer. Since the material having the absorption wavelength peak in a range of 700 nm or shorter can be visually detected, the secrecy cannot satisfactorily be maintained. If a material having the absorption wavelength peak in a range of 1100 nm or longer is used, sensitivity of a Si-type photo-detection device, such as a CCD, deteriorates. In this case, the identification mark cannot accurately be judged. It is further preferable to employ a absorption coloring material or pigment having the absorption wavelength peak in a range of 1000 nm or shorter. The material of a type in which the near infrared absorption coloring material is dispersed or mixed in the binder may be used while being combined with a usual coloring material or pigment. It is preferable that the near infrared absorption coloring material do not absorb the exciting wavelength for the near infrared fluorescent coloring material. The inhibition of the absorption of visible rays enables covering and improves the confidentiality of the copy inhibition function. Specifically, the near infrared absorption coloring material or pigment that can be used is as follows. However, a material which can be absorbed in the infrared region, which has a large absorption coefficient and which exhibits excellent weather and light resisntace. Compounds (62) to (126) The binder resin for use in the foregoing near infrared absorption coloring material or pigment may be a urea resin, melamine resin, alkyd resin, acryl resin, vinyl chloride resin, aromatic sulfonamide resin, or a benzoquanamine resin or their copolymer. By using an ultraviolet absorber or an anti-oxidant in the resin, the weather resistance of the resin can be improved. The resin can be manufactured by a block resin crushing method, emulsification Polymerizing method or a resin precipitation method or the like. The maximal wavelength of the fluorescent spectrum of the near infrared fluorescent coloring material or pigment and the maximal wavelength of the absorption spectrum of the near infrared absorption coloring material must be the same. In usual, the difference between them is 100 nm or shorter, more preferably 50 nm or shorter. If the maximal wavelength of the fluorescent spectral and that of the absorption spectral are different from each other by 100 nm or more, the transmission wavelength region of the CCD for detecting the near infrared rays is enlarged excessively, causing the contrast to be lowered undesirably. Fig. 1 is a graph of a reflectance of a copying paper for a copying machine. Since the copying paper has a substantially constant reflectance in a range from 450 to 1200 nm, it is preferable to be used as a medium in this embodiment. Although a copying machine will now be described as an example of a detection apparatus in this embodiment, other embodiments are possible, of course, such as an image scanner. Fig. 2 is a schematic view which illustrates the copying machine according to the present embodiment. Referring to Fig. 2, reference numeral 201 represents an image scanner portion for reading an original document and performing a digital signal process. Reference numeral 200 represents a printer portion for transmitting a full color image corresponding to the image of an original document read by the image scanner 201 on to paper. In the image scanner portion 201, reference numeral 202 represents a thick plate for an original document for securing an original document 204 placed on an original document retainer glass (hereinafter called a platen) 203. The original document 204 is irradiated with light emitted from a halogen lamp 205. Light reflected by the original document 204 is introduced by mirrors 206 and 207 so that an image is, by a lens 208, formed on a four-line sensor (hereinafter called a "CCD") composed of four line CCD line sensors. The CCD 210 decomposes the color of optical information of the original document to transmit, to a signal processing portion 209, red (R), green (G) and blue (B) components of full color information and infrared ray information (IR) component. The elements 205 and 206 are moved mechanically at speed v and the element 207 is moved also mechanically at speed 1/2v in a vertical direction (hereinafter a "sub-scan direction") with respect to the electrical scan direction (hereinafter called a "main scan direction) of the line sensor so that the overall surface of the original document is scanned. Reference numeral 211 represents a standard white plate for generating data for correcting read data corresponding to the line sensors 210-1 to 210-4 for IR, R, G and B components when shading correction is performed. The standard white plate has substantially uniform reflecting characteristics with respect to visible rays to infrared rays as shown in Fig. 3, the standard white plate being white with respect to visible rays. The standard white plate is used to correct data transmitted from the IR sensor 210-1 with respect to infrared rays and data transmitted from the R, G, and B visible-ray sensors 210-2 to 210-4. The signal processing portion 209 electrically processes the read signal to decompose the signal into magenta (M), cyan (C), yellow (Y) and black (BK) components which are then transmitted to the printer portion 200. One of the M, C, Y and BK components is plane-sequentially transmitted to the printer 200 whenever the image scanner portion 201 scans the original document. When the original document has been scanned four times, a color image can be formed. The M, C, Y and BK image signals transmitted from the image scanner portion 201 are transmitted to a laser driver 212. The laser driver 212 modulates and operates a semiconductor laser 213 in response to the image signals. Laser beams are allowed to pass through a polygonal mirror 214, a f- lens 215, and the mirror 216 as to scan the surface of a photosensitive drum 217. Reference numerals 219 to 222 represent developing units comprising a magenta developing unit 219, a cyan developing unit 220, a yellow developing unit 221 and a black developing unit 222. The four developing units 219 to 222 alternately come in contact with the photosensitive drum so that M, C, Y and BK electrostatic latent images formed on the photosensitive drum 217 are developed by corresponding toners. Reference numeral 223 represents a transfer drum for winding paper supplied from a paper cassette 224 or 225 around a transfer drum 223 to transfer a toner image developed on the photosensitive drum 217 on to the paper. Thus, the four colors, that is, M, C, Y and BK are sequentially transferred, and then the paper is allowed to pass through a fixing unit 226 before it is discharged. The halogen lamp-205 is commonly used to read visible ray information and to read infrared ray information, the halogen lamp 205 having both irradiation wavelength components required to read the two types of information items. By using the common irradiation system as described above, irradiation light beams having different wavelength components for reading visible and infrared rays information are effectively applied to the original document. Fig. 4A illustrates the structure of the CCD 210 for use in this embodiment. Referring to Fig. 4A, reference numeral 210-1 represents a light receiving device array for reading infrared ray (IR), and 210-2, 210-3 and 210-4 represent light receiving device arrays for respectively reading R, G and B wavelength components. The IR, R, G and B sensors 210-1 to 210-4 respectively have openings having a diameter of 10 µm in the main scan direction and the sub-scan direction. The four light receiving device arrays having different optical characteristics are disposed on the same silicon chip in a monolithic manner so that the IR, R, G and B sensors are disposed in parallel to each other to read the same line of the original document. By using the CCD constituted as described above, the common optical system, such as the lens, can be used to read the visible rays and infrared rays. As a result, accuracy in the optical adjustment can be improved and the adjustment can easily be completed. Reference numeral 210-5 represents a glass plate having a characteristic capable of cutting infrared rays in the diagonal line section thereof, the glass plate 210-5 having a thickness of about 300 µm. The characteristic of cutting infrared rays is realized in the diagonal line section due to a diachronic mirror 210-11. The characteristic of cutting infrared rays is shown in Fig. 5. The glass plate is bonded to the surface of the chip in such a manner that the evaporated surface of the glass plate faces the sensor side. Fig. 4B is an enlarged view which illustrates the light receiving device. Each sensor has a length of 10 µm per length in the main scan direction. Each sensor includes 5,000 pixels in the main scan direction as to read the shorter side direction (297 mm) of an A3-size original document at a resolving power of 40 dpi. The R, G and B sensors are disposed at a line interval of 80 µm while being disposed at each 8 lines when the resolving power in the sub-scan direction is 400 lpi (line per inch). The line interval between the IR sensor 210-1 and the R sensor 210-2 is made to be 160 µm (16 lines) which is twice the other line interval. As a result of the foregoing structure in which the interval between the IR sensor 210-1 and the R sensor 210-2 is made to be longer than the interval between the other sensors, the evaporated surface 210-11 of the glass plate 210-5 can be made to face the sensors 210-2 to 210-4 while making the non-evaporated portion to face the sensor 210-1 at a low fastening position accuracy at the time of bonding the glass plate 210-5 to the surface of the chip. The glass plate 210-5 is fastened adjacent to the sensor surface, while the evaporated film 210-11 for blocking infrared rays is fastened to face the sensor. The reason for this is that light beams passing toward the sensor are converged by the lens 209 and therefore the light beams passing toward the sensors are superposed at a position distant from the surface of the sensor as shown in Fig. 6. That is, if the infrared ray cutting filter 210-11 is made to filter only light beams passing toward the sensors 210-2 to 210-4, the infrared ray cutting filter 210-11 must be fastened to a position adjacent to the sensor at which the IR light beam and the R light beam are not superposed. The arrangement made in such a manner that the infrared ray cutting filter 210-11 is disposed adjacent to the surface of the sensor enables the allowable width a for fitting the IR filter between the IR light beams and the R light beams to be widened. Therefore, the accuracy for fitting the glass plate 210-13 to the sensor chip can be lowered. If the infrared ray cutting filter is fastened to the surface of the glass plate 210-5 opposing the sensor, the IR light beams and the R light beams are superposed. As a result, if the infrared ray cutting filter is disposed to sufficiently filter the R light beams, a major portion of the IR light beams focused on to the IR sensor 210-1 is undesirably cut, causing the level of the IR signal to be lowered excessively. As an alternative to the structure in which the glass plate 210-5 is fastened as shown in Fig. 7, the infrared ray cutting filter 210-11 may be disposed on the surface of the cover glass 210-13 facing the sensor. In this case, the distance d from the surface of the sensor to the internal surface of the cover glass must sufficiently be shortened by constituting a ceramic package 210-12 of the CCD sensor so that the infrared ray cutting filter 210-11 disposed on the internal surface of the cover glass does not substantially interrupt the IR light beams. With reference to Fig. 8, the filter spectrum characteristic of the IR, R, G and B line sensors of the CCD 210 will now be described. The characteristics R has sensitivity with respect to light beams in the red wavelength region and the infrared ray wavelength region. The characteristics G has sensitivity with respect to light beams in the green wavelength region and the infrared wavelength region. The characteristics B has sensitivity with respect to light beams in the blue wavelength region and the infrared wavelength region. Since filters 210-6 and 210-7 are superposed on the IR sensor 210-1, the IR sensor 210-1 has sensitivity with respect to infrared light beams represented by the diagonal lines shown in Fig. 8. As can be understood from Fig. 8, the R, G and B filters 210-8 to 210-10 have sensitivity with respect to infrared rays in a range of 700 nm or longer. Therefore, the infrared ray cutting filter 210-11 has characteristics shown in Fig.5. Fig. 9 shows spectrum absorption ratio of an infrared ray absorber SIR-159 manufactured by Mitsui Toatsu for used to form a detection mark of a specific original document according to this embodiment. This embodiment is arranged in such a manner that the presence of the infrared ray absorber is read by the IR sensor that is arranged to detect only infrared rays ranging from 750 nm to 850 nm. In order to achieve this, a far infrared ray cutting filter of a diachronic mirror as shown in Fig. 10 is disposed on the lens 208. Since the foregoing filter does not adversely affect the R, G and B sensors 210-2 to 210-4 as well as the IR sensor 210-1, it is disposed in the lens portion commonly provided for the visible rays and infrared rays. As a result, the filter to be fastened to the lens 208 can be designed to simply have the far infrared ray cutting characteristics. Therefore, excellent far infrared ray cutting characteristics can be realized by a simple interference film structure. Figs. 11A and 11B are block diagrams which illustrates the flow of an image signal in the image scanner portion 201. The image signal transmitted from the CCD 210 is received by an analog signal processing portion 3001 as to be subjected to a gain adjustment and an offset adjustment, and then converted by A/D converters 3002 to 3005 into 8-bit digital image signals for each color signal. Then, the image signal is supplied to shading correction portions 3006 to 3009 as to be subjected to a known shading correction using a read signal of the standard while plate 211 for each color. Reference numeral 3019 represents a clock generating portion for generating clocks in a pixel unit. Reference numeral 3020 represents a line counter for counting clocks to generate a pixel address output for one line. Reference numeral 3021 represents a decoder for decoding main scan address supplied from the main scan address counter 3020 to generate CCD drive signals, such as shift pulses and reset pulses, VE signals representing an effective region in a read signal for one line supplied from the CCD, and a line synchronizing signal HSYNC. The counter 3020 is cleared in response to the HSYNC signal to start counting the main scan address of the next line. Since the light receiving portions 210-1, 210-2, 210-3 and 210-4 of the CCD 210 are disposed while having predetermined intervals, the spatial deviation in the sub-scan direction is corrected in line delay devices 3010, 3011 and 3012. Specifically, the IR, R, and G signals for reading information about the original document in the sub-scan direction with respect to the B signal are line-delayed in the sub-scan direction to be made coincide with the B signal. Reference numerals 3013, 3014 and 3015 represent light quantity/density conversion portion each comprising a look up table ROM to convert R, G and B brightness signals into C, M and Y density signals. Reference numeral 3016 represents a known masking and UCR circuit which receives three primary color signals Y, M and C to sequentially transmit Y, M, C and Bk signals while having a predetermined bit length, for example, 8 bits whenever a reading operation is performed. Reference numeral 3 represents an identifying portion for detecting a specific pattern in the original document. Reference numeral 3018 represents a CPU portion for controlling an optical system for reading the original document, controlling the sequence for controlling the operation for turning on/off an original document irradiation lamp 205 and generating a pixel region signal VSYNC in the sub-scanning direction. In accordance with the result of judgment supplied from the recognition portion 3, the CPU portion 3018 controls a selector 3017 to transmit, to the printer, a port output in place of the read signal to inhibit the operation of copying the specific original document. Fig. 12 shows timings of the respective control signals. The VSYNC signal is an image effective region signal in the sub-scan direction as to be used to form sequential output signals (M), (C), (Y) and (Bk) with which the image is read in a region of "1". The VE signal is an image effective region signal in the main scan direction to arrange the balance of the main scan start position in the region of "1". The CLOCK signal is a pixel synchronizing signal which transfers image data at the first transition timing 0 → 1. The image pattern to be detected in this embodiment will now be described with reference to Figs. 13A and 13B. Figs. 13A and 13B illustrate near infrared absorbing coloring materials which do not absorb visible rays having the characteristics shown in Fig. 9 is used together with a coloring material which absorbs about 600 nm to record low reflectance portions 101. Near infrared fluorescent coloring material having characteristics shown in Fig. 14A is used in high reflectance portions 102. Since the high reflectance portions 102 are printed as small patterns in the form of squares each having a side of about 12.0 µm and they are substantially the same color in the visible region, the image pattern shown in Figs. 13A and 13B cannot be identified visually. However, it can be detected in an infrared region. Although a pattern in the form of a square having a side of about 120 µm is described as an example to make ensuing descriptions, the foregoing region has a size of about four pixels if the same is read at 400 dpi (dot per inch). It should be noted that the method of forming the pattern is not limited to the foregoing method. With reference to Fig.15, the identifying portion shown in Figs. 11A and 11B will now be described. Reference numerals 10-1 to 10-4 shown in Fig. 15 represent image data line delay portions each comprising a FIFO. An address pointer is initialized in response to a line synchronizing signal HSYNC (omitted from illustration), while data is written or read for pixel unit in response to the CLOCK signal. Each of the image data line delay portions 10-1 to 10-4 delay R, G, B and IR data of 32 bits by one line. First, an input signal is held in flip flops 11-1 and 11-2 to be delayed for two pixels to generate data for pixel A. Further, the line memories 10-1 and 10-2 delay the data for two lines to generate data for pixel C. Data items for the pixel C respectively are delayed by two pixels and four pixels to generate data about subject pixel data X and data about pixel B. Similarly, data about pixel D is supplied to a judging portion 12. The position relationship among the pixels A, B, C and D around the subject pixel X is as shown in Fig. 16. That is, if the subject pixel X is reading the low reflectance portion 101 shown in Figs. 13A and 13B, the pixels A, B, C and D are reading the pixels of the patterns positioned around the low reflectance portion 101. A judgment algorithm set to the judging portion 12 according to this embodiment will now be described. Assuming that R, G, B and IR components of the reading signal which forms the pixel signal for A are AR, AG, AB and AIR and pixels signals for B, C and D are defined, average values YR, YG, YB and YIR of the read signals for each color component R, G, B and IR in each pixel signal are defined by the following equations: Y R = 1 4 (A R + B R + C R + D R ) Y G = 1 4 (A G + B G + C G + D G ) Y B = 1 4 (A B + B B + C B + D B ) Y IR = 1 4 (A IR + B IR + C IR + D IR ) An aimed pattern is judged in accordance with the difference between average value Y obtained by the foregoing equation and the subject pixel X. That is, assuming that the R, G, B and IR components of X are XR, XG, XB and XIR respectively, the following relationships are held: ΔR = |Y R - X R | ΔG = |Y G - X G | ΔB = |Y B - X B | ΔIR = |Y IR - X IR | If the following relationships are held, a judgment may be made (subject to further conditions) that a pattern is present: ΔR < K and ΔG < K and ΔB < K and ΔIR > L1 or Y IR /X IR > L2 where K, L1 and L2 are constants. That is, if the color tone is not considerably different in the visible region (smaller than K) between the subject pixel X and the adjacent pixels A, B, and C and D and if the difference is larger by the constant L1 in the infrared region, or if the ratio of the level of the subject pixel X and that of the adjacent pixels is larger than the constant L2, a judgment may be made (subject to further conditions) that a specific pattern is present. The reason why the ratio is used as well as the judgment of the infrared region is that the deterioration in the infrared ray signal level due to contamination of the original document must be compensated. In this embodiment, the overall damping of the infrared ray read signal due to the influence of contamination is compensated by detecting the ratio. When reading operations 103, 104 and 105 are performed in different scan directions as shown in Fig. 13A, the intensities of the IR signals respectively are as shown in Fig. 13B so that the low reflectance portion, the reflectance portion of the medium and the high reflectance portion are detected. Therefore, a judgment is made that the pattern is present and the recognition rate is improved while performing together the foregoing relationships. Fig. 17 illustrates the structure of the judgment portion 12 adapted to the foregoing relationships. An adder 121 simply adds the color components for four pixels to transmit the upper eight bits to obtain YR, YG, YB and YIR. A subtractor 122 obtains the difference from each component of the subject pixel signal to supply upper five bits of the components ΔR, ΔG and ΔB to a judgment LUT 128 comprising a ROM. If each of the upper five bits is smaller than constant K, 1 is transmitted from the LUT 128. Similarly, 8-bit YIR and XIR are supplied to an address terminal of a judgment LUT comprising a ROM in a case of an infrared read signal. If the judgment AIR > L1 or YIR/XIR > L2 is resulted in the foregoing calculation ΔIR = YIR - XIR, l is transmitted from the LUT 129. The logical product of the output from each LUT is calculated in-an AND gate 130, and therefore the fact that the relationships hold can be detected if 1 is obtained at the output terminal of the AND gate 130. The result is supplied to a latch 3022 shown in Figs.11A and 11B. The latch output is supplied to an input port P10 of a CPU 3018. The CPU clears the latch 3022 in response to a signal of an output port P9 prior to starting the copying sequence. A usual copying operation and an operation of the CPU to determine if the relationships above hold will now be described with reference to Fig. 18. When an operator places the original document 204 on the platen 203 and starts the copying operation by operating a control portion (omitted from illustration), the CPU 3018 controls a motor (omitted from illustration) to move the reflecting mirror 206 to a position below the standard white plate 211. Then, the halogen lamp 205 is lit on to irradiate the standard white plate 211 so that the shading correction portions 3006 to 3009 sample shading data for the IR, R, G and B signals (step 1). Then, the port output P9 is made to be zero, the output from the latch 3022 is made to be zero-cleared, the output from P8 is made to be zero, input A of the selector 3017 is selected so that a masked and UCR-processed image signal is supplied to the printer. Then, the output from P9 is made to be 1, and the clearing operation of the latch 3022 is completed (step 2). Then, the original document is read four times to correspond to the operation of recording the four colors M, C, Y and BK performed in the printer portion so that the image is recorded. Further, whether the relationships hold is detected. First, a magenta image is recorded in such a manner that the CPU qualifies the processing condition for processing the magenta image to be performed by the masking and UCR processing portion to cause the optical system to perform the scanning operation and to supply a magenta signal to the printer. After the scanning operation has been completed, the CPU returns the optical system to the scan start position (step 3). The CPU periodically reads the port 10 during the operation of reading the original document to judge whether or not the input to the port 10 is 1. If the P10 is 1, a judgment is made that the relationships above hold. Similarly, recording of cyan, yellow and black data is controlled in steps 4 to 6, and the CPU periodically examines the state of P10. If the output from P10 is 1, a judgment is made that the relationships above hold. Second Embodiment Figs. 19A and 19B illustrate an example of a structure of an image reading apparatus in a second embodiment. A CCD is, as shown in Fig. 19A, is arranged in such a manner that two-line sensors are formed on a common silicon chip in a monolithic manner. A line sensor 3301-1 is an infrared ray reading sensor (an IR sensor), and a line sensor 3301-2 is a full color line sensor in which R, G and B sensors are alternately disposed in pixel units. A glass plate 3301-5 having a dichroic filter 3301-11 for cutting infrared rays evaporated thereof is fastened on to the foregoing sensor by a method similar to that shown in Figs.4A and 4B. The dichroic filter 3301-11 has the infrared ray cutting characteristics shown in Fig. 5 similarly to 210-11. The glass plate is fastened to the CCD chip similarly to the method shown in Figs. 4A and 4B such that the end of the evaporated portion is positioned between the line sensors 3301-1 and 3301-2. Fig. 19B is an enlarged view which illustrates pixels of the line sensors 3301-1 and 3301-2. The IR sensor 3301-1 has a pixel size 18 µm x 18 µm and in which R and B filters having characteristics shown in Fig. 8 are superposed on the sensor, the IR sensor 3301-1 having the infrared ray transmission characteristics of the IR sensor 210-1. By combining the IR sensor 3301-1 with a far infrared ray cutting filter disposed in the imaging optical system similar to that according to the first embodiment and having the characteristics shown in Fig. 10, infrared ray reading characteristics similar to that according to the first embodiment are attained. Reference numeral 3301-2 represents R, G and B sensor arrays positioned away from the IR sensor by 180 µm (for 10 lines), the sensor array 3301-2 having an arrangement in which R, G and B pixels having a size of 6 µm to correspond to the size of 18 mm of one pixel of the IR sensor in the main scan direction. Each of the R, G and B pixels is provided with a color decomposing filter having the characteristics shown in Fig. 8. The sensor according to this embodiment has 5,000 pixels in the main scan direction to read an A3-size original document at 400 dpi, and 5,000 combinations of R, G and B are provided. In order to project the size 63.5 µm (one pixel of 400 dpi) of the original document retainer onto a size of 18.5 µm, the contraction ratio of the optical system is made to be 18.5/63.5. When the identification pattern according to the first embodiment was measured by the foregoing detection apparatus, an excellent judgment was performed. Third Embodiment Figs. 20A and 20B illustrate an example of the structure of an image reading apparatus in a third embodiment. A CCD 3401 comprises a sensor 3402 having R, G, B and IR pixels formed on lines as shown in Fig. 20A so that image data for one pixel is color-decomposed (the wavelength is decomposed) by the combination of IR, R, G and B to read the image data. Each of the IR, R, G and B pixels has a size of 63.5/4 µm in the main scan direction so that a pixel of 63.5 µm is read by a combination of IR, R, G and B. Since the sensor according to this embodiment reads an original document at 400 dpi, the contraction ratio of an optical system is made to be one time so that the size 63.5 µm (one pixel of 400 dpi) of the original document retainer is projected onto the size of 63.5 µm. The IR reading pixel has R and B filters having the characteristics shown in Fig. 8 and superposed on the sensor to have the infrared ray transmission characteristics of the IR sensor 210-1. By combining it with the far infrared ray cutting filter disposed in the imaging optical system (omitted from illustration) and having the characteristics shown in Fig. 10, the infrared ray reading characteristics similar to that obtainable from that according to the first embodiment can be attained. The R, G and B reading pixels have color decomposing filters having the characteristics shown in Fig. 8. A glass plate 3403 having dichroic filters 3403-11 for cutting infrared rays, evaporated at a pitch of 63.5 µm and having a width of 63.5/4 µm is fastened on the sensor as shown in Fig. 20A. The dichroic filter 3404 has the infrared ray cutting characteristics similarly to 210-11. The glass plate is fastened to the CCD chip similarly to that shown in Figs.4A and 4B in such a manner that its evaporated side faces the surface of the chip and the portion, which is not evaporated, corresponds to the IR pixels as shown in Figs. 20A and 20B. When the identification pattern according to the first embodiment was measured with the foregoing detection apparatus, an excellent judgment was performed. Although the third embodiment is arranged in such a manner that the IR, R, G and B pixels for reading one pixel are arranged in the main scan direction, another structure may be employed which is arranged in such a manner that they are disposed in a 2D manner and the infrared ray cutting dichroic filters are disposed in only the portions of the glass plate that correspond to the R, G and B pixels. Although the foregoing embodiment is arranged in such a manner that the infrared ray cutting filter is made of transparent material and it is fastened to the sensor, the filter is not limited to the infrared ray cutting filter. The filter may be a filter for cutting ultraviolet rays that are not required to read visible information. As described above, use of the invisible information recorded medium having the identification mark composed of a region having a high reflectance and a region having a low reflectance region as compared with the reflectance of the medium at the same near infrared ray wavelength and an apparatus for detecting the invisible information recording medium enables the specific original document to be judged assuredly while reducing the cost. Further, an attempt of judgment prevention using the infrared ray absorbing film or an infrared reflecting film can assuredly be judged.

Claims: Apparatus for detecting copy-prohibited documents by means of an invisible identification mark (101, 102) on the documents, characterised by : detecting means (10, 11, 12) for detecting first regions (101) on a document which return a lower intensity than the document medium when regarded in a near infra-red waveband and second, different regions (102) on the document which return a higher intensity than the document medium when regarded in the same near infra-red waveband; and judging means (12) for judging whether the document is copy-prohibited in dependence upon whether both the first and second regions are detected in a scanning direction separated by regions having the intensity of the medium. Apparatus according to claim 1, wherein the first regions are formed from a material having an absorption peak in the near infra-red waveband, and the second regions are formed from a fluorescent material having a fluorescence peak in the near infra-red waveband. Apparatus according to claim 2, wherein the excitation wavelength of the fluorescent material lies outside the visible range. Apparatus according to claim 2 or claim 3, further comprising illuminating means for illuminating a document with light to read visible information and exciting light to cause fluorescence of the fluorescent material. A method of detecting copy-prohibited documents by means of an invisible identification mark (101, 102) on the documents, characterised by : detecting whether first regions (101) exist on a document which return a lower intensity than the document medium when regarded in a near infra-red waveband; detecting whether second, different regions (102) exist on the document which return a higher intensity than the document medium when regarded in the same near infra-red waveband; and judging whether the document is copy-prohibited in dependence upon whether both the first and second regions are detected in a scanning direction separated by regions having the intensity of the medium. A method according to claim 5, wherein the first regions are formed from a material having an absorption peak in the near infra-red waveband, and the second regions are formed from a fluorescent material having a fluorescence peak in the near infra-red waveband, the document being illuminated with exciting light to cause said fluorescence.

Inventors: ARIMOTO SHINOBU, HAYASHI TOSHIO, NAGASE TETSUYA, NAKAI TAKEHIKO, SASANUMA NOBUATSU, TANIOKA HIROSHI, UTAGAWA TSUTOMU, YOSHINAGA KAZUO, ARIMOTO, SHINOBU, HAYASHI, TOSHIO, NAGASE, TETSUYA, NAKAI, TAKEHIKO, SASANUMA, NOBUATSU, TANIOKA, HIROSHI, UTAGAWA, TSUTOMU, YOSHINAGA, KAZUO, ARIMOTO, SHINOBU, C/O CANON KABUSHIKI KAISHA, HAYASHI, TOSHIO, C/O CANON KABUSHIKI KAISHA, NAGASE, TETSUYA, C/O CANON KABUSHIKI KAISHA, NAKAI, TAKEHIKO, C/O CANON KABUSHIKI KAISHA, SASANUMA, NOBUATSU, C/O CANON KABUSHIKI KAISHA, TANIOKA, HIROSHI, C/O CANON KABUSHIKI KAISHA, UTAGAWA, TSUTOMU, C/O CANON KABUSHIKI KAISHA, YOSHINAGA, KAZUO, C/O CANON KABUSHIKI KAISHA
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1994
Main classification: B41M3
IPC codes: G03G21, H04N1, G07D7, G03G9, B42D15